MEP-002A and MEP-003A Replacement Oil Pressure Switch

[mistaken1]

Well I went to exercise the MEP-002A on Sunday before the big storm and needless to stay it suddenly died.

It wants to start right up but as soon as I let go of the starter switch it dies. If I hold the starter switch in the start position it runs.

It had only been running 15 minutes or so and it was cold outside (still is) so I do not think that the temperature switch is the culprit.

The oil pressure gauge showed 30# when running and would quickly return to 30# when the start switch is held. So I jumpered out the low oil pressure switch and wouldn't you know it the unit runs with the same 30# of pressure on the gauge. (the gauge started out at 0# and went to just over 35# when first started and then as the unit warmed settled down to its normal 30#).

So either my gauge is bad and pressure switch is saving my engine or my gauge is accurate and my pressure switch is broken (or clogged).

On to my questions to those with more experience:

Which is more likely to be broken the gauge or the pressure switch?

I am assuming the pressure switch and am looking for another and this is what I find.

5930-01-039-3140 Master Cross Reference Data
​

Mfg. Part Number
​

3090177
76052-14
C0309017700
M-1423-14-S2
M-4008-14
M1423-14
SM-2A-14F
​

I have not had any luck finding any of these exact numbers but I did find some things that are close to the Hobbs M-4008-14 and by close I mean I see no reason why they will not work but again want the feedback of those more experienced.

The Hobbs 76052-15 is a SPST NO screw terminal pressure switch (1/8-27 NPT) that is adjustable between 14 and 24 psi and is factory set at 15 psi.

Will this Hobbs 76052-15 work as a replacement for the original Hobbs M-4008-14?

76052-15 - Hobbs (replaces 4008-15) | Translectric, Inc. The Heavy Duty Parts Pros

HONEYWELL HOBBS 76052-15 is in stock|Buy7605215|76052 15|Onlinecomponents.com

Thanks in advance.

 

[coyote62ny]

give tom Badgett at gulf coast trucks a call he has lots of parts for these gen sets office number is 1-281-422-3200 cell 1-832-323-1445 most of his parts are used but he tests them on a gen set before he ships them and very reasonable on prices as well hope this helps you out

 

[LuckyDog]

Which is more likely to be broken the gauge or the pressure switch?

I am assuming the pressure switch ...

I agree the pressure switch is broken. If the guage were broken, it wouldn't very likely be moving in a correct manner; if at all. The guage isn't very accurate but 35 at start when cold and becoming 30 when warm sounds good to me.

 

[Speddmon]

As long as the presure switch threads into the place of the original, or you can get adapters to make it thread in, get it and use it.

The 15 pound setting might be just a bit higher than the stock one, but that's just a bit more protection (and maybe a bit harder to start on really cold days).

Edit: The factory installed pressure switch is set at 14 pounds +/- 2 pounds. So the replacement switch you found should work out just fine.

 

[PeterD]

Just a side thought, but many GM vehicles (and earlier Hummer H1s) use an oil pressure switch that is normally open at zero pressure and closes the contact at about 6 to 8 PSI. This switch drives the fuel lift pump on Hummer's diesel engine. I'd be glad to post a CarQuest number if anyone is interested, but it would require a connector/pigtail to use, not difficult however.

 

[mistaken1]

Shortly after starting this thread I ordered a "Hobbs part number M4008 15 NO. This Switch is a NOS unit I purchased from the large online auction site for $20.26 delivered.

I finally installed it today. The generator started and ran without issue. I put a 1500 watt heater on one of the 240V legs and let it run for 30 minutes.

As I understand it this NOS switch is very similar to the new models I posted earlier. It is a 15 lbs normally open pressure switch.

 

[Keith_J]

This switch is inoperative on my 002A. Took me an hour to trace it all down since I was working alone. The rubber cap over the atmospheric port was askew but removing, cleaning and replacing didn't help. I've eliminated it from the system since I cannot get the old one off without fear of stripping the hex flats.

Since it is not leaking, I am thinking of teeing off the line to the pressure gauge for a new one if the old one cannot be removed. Yes, I am watching the pressure gauge like a hawk. It starts at 45 PSI and drops to 40 PSI when running. Far more than the recommended 10 PSI pre 1000 RPM.

I cannot believe the last mechanic to service this machine installed the oil filter all wrong. They put the rubber gasket OUTSIDE on the bolt and nothing inside. The shell gasket was twisted and over-tightened. Fortunately, the oil looked like it has been run 5 minutes. It has new filter and gaskets, o-ring on the shell. Makes install so much easier. Same on the fuel filters.

New switch can be obtained here:http://www.mixerandplantparts.com/product-p/14242.htm

Appears to be identical to the one on the generator.

 

[Keith_J]

I tried to get the switch to work by pulling a vacuum on the outer port so I pulled it. Had to use curved jaw Vise Grip locking pliers on the body to get it off while holding onto the 45 degree ell with an open end wrench.

I applied around 100 PSI of air to it, only sporadic continuity on my multimeter. I would like to see the failure mode since these are rather mission critical.

 

[Keith_J]

Found the issue. The problem is the engine stop solenoid (governor solenoid, K5 per the TM. Most here are familiar with inrush current on motor starting. On solenoids running direct current, inrush is an issue but limited by the resistance of the wiring supplying the current. The same phenomenon gives rise to "outrush" or back electromotive force. When a solenoid is deenergized, the collapsing magnetic field causes a reverse current in the attached leads. This happens every time the generator is stopped, eventually arcing the points in the switch. The problem is intensified because the radio frequency noise suppressors (capacitors) on the fuel pumps effectively make a tank circuit (LC circuit) which is "rung" every time the solenoid is deenergized. The residual energy in the solenoid is passed back and forth over the thermal and oil pressure cut-out switches until dissipated by resistance in the wiring.

Solution? Simple free-wheeling diode over the solenoid's terminals. The diode does nothing until the power to the solenoid is interrupted, either from the operator tripping the switch, the circuit breaker (CB2) is tripped or the safety switches trip. The diode then dumps current in the solenoid instead of the current back feeding into the safety switches, eventually arcing them into failure.

Allied Electronics has the switch so I was able to get data. It is rated for 4 amperes at 24 volts DC. plenty for the 1/3 ampere the governor solenoid draws. But when deenergized, the coil in the solenoid can send a power surge of 30 amperes or more for a millisecond or so. That is what kills this switch.

http://en.wikipedia.org/wiki/Flyback_diode

Installing the diode is easy, just connect the cathode to P66H16 wire, terminal 1 of the solenoid and the anode to P55T16, terminal 2 of the solenoid. Use a 1N004. Cathode is the bar, anode is the triangle. If you get it wrong, it might pop the circuit breaker. Or probably, will fry the diode.